This invention relates generally to heterocyclic compounds useful as ashless oil-soluble additives for lubricating oils.
Zinc dialkyldithiophosphates (ZDDP) are widely used as lubricant additives. The principal disadvantages of these compounds are that an ash residue is produced by the zinc as the additive is consumed, and that phosphorus is known to affect the efficiency of catalytic converters in motor vehicles, thereby causing emissions problems. An ashless, non-phosphorus alternative to ZDDP would be extremely useful.
Dithiohydantoin compounds are disclosed in European Patent Application No. EP 0 728 747 A1. However, the compounds are not within the scope of the present invention, and moreover, are disclosed only for pharmaceutical applications.
The problem addressed by this invention is to find improved phosphorus-free ashless oil-soluble additives for lubricating oils.
The present invention is directed to a compound of formula I: 
wherein W represents O, Sxe2x80x94A2, or two groups, R3 and R4; bonds a and b are single or double bonds, provided that one of a and b is a single bond and the other is a double bond; c is a single or double bond, and d is a single bond, double bond, or two single bonds, provided that d is a single bond when c is a double bond, d is not a single bond when c is a single bond, and W is R3 and R4 when d is two single bonds;
A1, A2, B1 and B2 are independently hydrogen, alkyl, alkenyl, aralkyl or one of the groups depicted in Scheme 1:
provided that B1 is absent when b is a double bond, B2 is absent when a is a double bond, A1 is absent when c is a double bond and A2 is absent when d is a double bond; and provided that A2 or B2 is not aralkyl when W is O or Sxe2x80x94A2;
R1, R2, R3 and R4 are independently hydrogen, alkyl, alkenyl, aryl or aralkyl; or R1 and R2, or R3 and R4, combine with the carbon atom to which they are attached to form an alkyl or alkenyl ring; Y is O or S; Z is O, S or NR9; m is 0 when bond e is a double bond and 1 when e is a single bond; n is 1 when bond f is a double bond and 2 when f is a single bond; R5 is C(Y)ZR7, hydrogen or C1-C4 alkyl; R6 is hydrogen or C1-C4 alkyl; R7, R8 and R9 are independently hydrogen, alkyl, alkenyl, aryl or aralkyl;
provided that at least one of A1, A2, B1 and B2 is present and is not hydrogen.
The present invention is further directed to a composition comprising a lubricating oil and from 0.1 to 20% of a compound of formula I; and to a method for improving the anti-wear and anti-corrosion characteristics of a lubricating oil by adding from 0.1 to 20% of a compound of formula I.
An xe2x80x9calkylxe2x80x9d group is a hydrocarbyl group having from one to twenty carbon atoms in a linear, branched or cyclic arrangement, and having from 0 to 2 oxygen, nitrogen or sulfur atoms. Substitution on alkyl groups of one or more halo, hydroxy, alkoxy, alkanoyl or amido groups is permitted; alkoxy, alkanoyl and amido groups may in turn be substituted by one or more halo substituents. Preferably, alkyl groups contain from one to twelve carbon atoms and from 0 to 1 oxygen, nitrogen or sulfur atoms. An xe2x80x9calkenylxe2x80x9d group is an xe2x80x9calkylxe2x80x9d group in which at least one single bond has been replaced with a double bond. An xe2x80x9carylxe2x80x9d group is a substituent derived from an aromatic compound, including heterocyclic aromatic compounds having heteroatoms chosen from among nitrogen, oxygen and sulfur. An aryl group has a total of from five to twenty ring atoms, and has one or more rings which are separate or fused. Substitution on aryl groups of one or more halo, alkyl, alkenyl, hydroxy, alkoxy, alkanoyl or amido groups is permitted, with substitution by one or more halo groups being possible on alkyl, alkenyl, alkoxy, alkanoyl or amido groups. An xe2x80x9caralkylxe2x80x9d group is an xe2x80x9calkylxe2x80x9d group substituted by an xe2x80x9carylxe2x80x9d group.
In formula I and Scheme 1, the letter a, b, c, d, e or f represents the total bonding between the atoms adjacent to each letter, e.g., when xe2x80x9caxe2x80x9d represents a single bond, the sulfur atom and ring carbon to which it is attached are connected by a single bond. These letters are used in formula I to indicate that the compound may exist in different tautomeric forms, e.g., when the sulfur shown in formula I is substituted, i.e., B2 is present, a is a single bond, b is a double bond and B1 is absent, as will be understood by one skilled in the art. In the substituent groups of Scheme 1, e and f indicate whether the bond between the adjacent carbons is a single or double bond, which is determined by the alkylating agent used to introduce the substituent, as described hereinbelow.
It is preferred that at least one of A1, A2, B1 and B2 is present and is not hydrogen or methyl. It is also preferred that A1, A2, B1 and B2 are independently hydrogen or one of the three groups depicted in Scheme 1. It is also preferred that W is R3 and R4, and c is a single bond. It is also preferred that W is R3 and R4, c is a single bond, A1 is hydrogen, and B1 or B2 is one of the groups depicted in Scheme 1.
In one aspect of the invention, a tetraalkylimidazolidinethione (TAIT), or an imidazolidinethione having from one to three alkyl groups, is alkylated with an acrylate ester to produce a compound having a CHR5CHR6C(O)OR7 group, as shown below for R5xe2x95x90R6xe2x95x90H and R7=alkyl. If R1, R2, R3 and R4 are all methyl, the TAIT is known as TMIT. 
The extent of N-alkylation versus S-alkylation varies with the identity of the R groups on the imidazolidenethione ring and with the alkylating agent, as shown below in the Examples.
In another aspect of this invention, a TAIT or an imidazolidinethione having from one to three alkyl groups is alkylated with an alkyl propiolate to produce a compound in which the ester side chain has a carbon-carbon double bond. In another aspect of this invention, a TAIT or unsubstituted imidazolidinethione is alkylated with an imine, CH2xe2x95x90NR8. In another aspect of this invention, a TAIT or an imidazolidinethione having from one to three alkyl groups is alkylated with maleic or succinic anhydride to produce a compound having a C(O)CHxe2x95x90CHC(O)OH or C(O)CH2CH2C(O)H side chain, respectively, with alkylation occurring mainly on the sulfur.
In one embodiment of the invention, the group ZR7 in a CHR5CHR6C(Y)ZR7 side chain or a CHxe2x95x90CHC(Y)ZR7 side chain contains a thioethyl group, i.e., a group having the structure xe2x80x94CH2CH2Sxe2x80x94, where one of the CH2 and the sulfur is attached to the C(Y) functionality and the other is attached to an alkyl, alkenyl or aralkyl group. For example, ZR7 can be OCH2CH2Sxe2x80x94R, where R is alkyl, alkenyl or aralkyl; when Y is O, and R5 and R6 are H, the side chain is CH2CH2C(O)OCH2CH2Sxe2x80x94R.
In a preferred embodiment of the invention, from 0.1 to 10% of a compound of formula I is added to a lubricating oil. More preferably, from 0.5 to 10% of a compound of formula I is added to a lubricating oil, and most preferably, from 0.5 to 3%. A lubricating oil is a natural or synthetic oil, having suitable viscosity for use as a lubricant, or a mixture thereof.